A. Field of the Invention
This invention relates to the field of computerized techniques for orthodontic treatment planning for human patients. More particularly, the invention is directed to finding virtual tooth features, which are very helpful and used in planning orthodontic treatment, on a virtual three-dimensional model of dentition. The tooth features are determined automatically using the computerized techniques; and can be manually adjusted when necessary.
B. Description of Related Art
The traditional process of diagnosis and treatment planning for a patient with orthodontic problems or disease typically consists of the practitioner obtaining clinical history, medical history, dental history, and orthodontic history of the patient supplemented by 2D photographs, 2D radiographic images, CT scans, 2D and 3D scanned images, ultrasonic scanned images, and in general non-invasive and sometimes invasive images, plus video, audio, and a variety of communication records. Additionally, physical models, such as made from plaster of paris, of the patient's teeth are created from the impressions taken of the patient's upper and lower jaws. Often, such models are manually converted into teeth drawings by projecting teeth on drawing paper. Thus, there is a large volume of images and data involved in the diagnosis and treatment planning process. Furthermore, the information may require conversion from one form to another and selective reduction before it could become useful. There are some computerized tools available to aid the practitioner in these data conversion and reduction steps, for example to convert cephalometric x-rays (i.e., 2 dimensional x-ray photographs showing a lateral view of the head and jaws, including teeth) into points of interest with respect to soft tissue, hard tissue, etc., but they are limited in their functionalities and scope. Even then, there is a fairly substantial amount of manual work involved in these steps.
Consequently, the practitioner is left to mental visualization, chance process to select the treatment course that would supposedly work. Furthermore, the diagnosis process is some-what ad-hoc and the effectiveness of the treatment depends heavily upon the practitioner's level of experience. Often, due to the complexities of the detailed steps and the time consuming nature of them, some practitioners take a shortcut, relying predominantly on their intuition to select a treatment plan. For example, the diagnosis and treatment planning is often done by the practitioner on a sheet of acetate placed over the X-rays. All of these factors frequently contribute towards trial and error, hit-and-miss, lengthy and inefficient treatment plans that require numerous mid-course adjustments. While at the beginning of treatment things generally run well as all teeth start to move at least into the right direction, at the end of treatment a lot of time is lost by adaptations and corrections required due to the fact that the end result has not been properly planned at any point of time. By and large, this approach lacks reliability, reproducibility and precision. More over, there is no comprehensive way available to a practitioner to stage and simulate the treatment process in advance of the actual implementation to avoid the often hidden pitfalls. And the patient has no choice and does not know that treatment time could be significantly reduced if proper planning was done.
In recent years, computer-based approaches have been proposed for aiding orthodontists in their practice. See Andreiko, U.S. Pat. No. 6,015,289; Snow, U.S. Pat. No. 6,068,482; Kopelmann et al., U.S. Pat. No. 6,099,314; Doyle, et al., U.S. Pat. No. 5,879,158; Wu et al., U.S. Pat. No. 5,338,198, and Chisti et al., U.S. Pat. Nos. 5,975,893 and 6,227,850, the contents of each of which is incorporated by reference herein. Also see imaging and diagnostic software and other related products marketed by Dolphin Imaging, 6641 Independence Avenue, Canoga Park, Calif. 91303-2944.
U.S. Pat. No. 6,648,640 to Rubbert, et al. describes an interactive, computer based orthodontist treatment planning, appliance design and appliance manufacturing. A scanner is described which acquires images of the dentition, which are converted to three-dimensional frames of data. The data from the several frames are registered to each other to provide a complete three-dimensional virtual model of the dentition. Individual tooth objects are obtained from the virtual model. A computer-interactive software program provides for treatment planning, diagnosis and appliance design from the virtual tooth models. A desired occlusion for the patient is obtained from the treatment planning software. The virtual model of the desired occlusion and the virtual model of the original dentition provide a base of information for custom manufacture of an orthodontic appliance. A variety of possible appliance and appliance manufacturing systems are contemplated, including customized arch wires and customized devices for placement of off-the shelf brackets on the patient's dentition for housing the arch wires, and removable orthodontic appliances.
U.S. Pat. No. 6,632,089 to Rubbert, et al. describes an interactive, software-based treatment planning method to correct a malocclusion. The method can be performed on an orthodontic workstation in a clinic or at a remote location such as a lab or precision appliance-manufacturing center. The workstation stores a virtual three-dimensional model of the dentition of a patient and patient records. The virtual model is manipulated by the user to define a target situation for the patient, including a target arch-form and individual tooth positions in the arch-form. Parameters for an orthodontic appliance, such as the location of orthodontic brackets and resulting shape of an orthodontic arch wire, are obtained from the simulation of tooth movement to the target situation and the placement position of virtual brackets. The treatment planning can also be executed remotely by a precision appliance service center having access to the virtual model of the dentition. In the latter situation, the proposed treatment plan is sent to the clinic for review, and modification or approval by the orthodontist. The method is suitable for other orthodontic appliance systems, including removable appliances such as transparent aligning trays.
Other background references related to capturing three dimensional models of dentition and associated craniofacial structures include S. M. Yamany and A. A. Farag, “A System for Human Jaw Modeling Using Intra-Oral Images” in Proc. IEEE Eng. Med. Biol. Soc. (EMBS) Conf., Vol. 20, Hong Kong, October 1998, pp. 563-566; and M. Yamany, A. A. Farag, David Tasman, A. G. Farman, “A 3-D Reconstruction System for the Human Jaw Using a Sequence of Optical Images,” IEEE Transactions on Medical Imaging, Vol. 19, No. 5, May 2000, pp. 538-547. The contents of these references are incorporated by reference herein.
The technical literature further includes a body of literature describing the creation of 3D models of faces from photographs, and computerized facial animation and morphable modeling of faces. See, e.g., Pighin et al., Synthesizing Realistic Facial Expression from Photographs, Computer Graphics Proceedings SIGGRAPH '98, pp. 78-94 (1998); Pighin et al., Realistic Facial Animation Using Image-based 3D Morphing, Technical Report no. UW-CSE-97-01-03, University of Washington (May 9, 1997); and Blantz et al., A Morphable Model for The Synthesis of 3D Faces, Computer Graphics Proceedings SIGGRAPH '99 (August, 1999). The contents of these references are incorporated by reference herein.
Tooth features, such as the cusp tips, marginal ridges, central groove lines, buccal grooves, contact points, tooth axes system, etc. play key roles in defining some well established orthodontic treatment planning criteria such as: alignment, marginal ridges, buccolingual inclination, occlusal relationships, occlusal contacts, overjet, interproximal contacts, root angulation, etc. Indeed, the American Board of Orthodontics (ABO) has introduced an Objective Grading System (OGS) for evaluating the results of an orthodontic treatment once it is completed using these criteria. Alignment refers to an assessment of tooth alignment. In the anterior region, the incisal edges and lingual surfaces of the maxillary anterior teeth and the incisal edges and labial-incisal surfaces of the mandibular anterior teeth are chosen to assess anterior alignment. In the maxillary posterior region, the mesiodistal central groove of the premolars and molars is used to assess adequacy of alignment. In the mandibular arch, the buccal cusps of the premolars and molars are used to assess proper alignment. Marginal ridges are used to assess proper vertical positioning of the posterior teeth. If marginal ridges are at the same height, it will be easier to establish proper occlusal contacts, since some marginal ridges provide contact areas for opposing cusps. Buccolingual inclination is used to assess the buccolingual angulation of the posterior teeth. In order to establish proper occlusion in maximum intercuspation and avoid balancing interferences, there should not be a significant difference between the heights of the buccal and lingual cusps of the maxillary and mandibular molars and premolars. Occlusal relationship is used to assess the relative anteroposterior position of the maxillary and mandibular posterior teeth. The buccal cusps of the maxillary molars, premolars, and canines must properly align with the interproximal embrasures of the mandibular posterior teeth. The mesiobuccal cusp of the maxillary first molar must properly align with the buccal groove of the mandibular first molar. Occlusal contacts are measured to assess the adequacy of the posterior occlusion. Again, a major objective of orthodontic treatment is to establish maximum intercuspation of opposing teeth. Therefore, the functioning cusps are used to assess the adequacy of this criterion; i.e., the buccal cusps of the mandibular molars and premolars, and the lingual cusps of the maxillary molars and premolars. Overjet is used to assess the relative transverse to relationship of the posterior teeth, and the anteroposterior relationship of the anterior teeth. In the posterior region, the mandibular buccal cusps and maxillary lingual cusps are used to determine proper position within the fossae of the opposing arch. In the anterior region, the mandibular incisal edges should be in contact with the lingual surfaces of the maxillary anterior teeth. Interproximal contacts are used to determine if all spaces within the dental arch have been closed. Persistent spaces between teeth after orthodontic therapy are not only unesthetic, but can lead to food impaction. Root angulation is used to assess how well the roots of the teeth have been positioned relative to one another.
Traditionally, the tooth features discussed above are visually identified and marked by the practitioner; and various measurements related to the treatment criteria are performed manually using measuring instruments and gauges. The ABO has developed an orthodontic measuring gauge to assist in the manual measurement of parameters related to the OGS criteria discussed above from the dental cast and the panoramic radiograph. Although the measuring gauges introduce a degree of consistency in the measurements when performed by different people, the measurements are still limited in scope to two-dimensional analysis.
Therefore, in order to enable computerized orthodontic treatment planning, and three-dimensional, accurate measurements of the criteria such as those developed by ABO, there is a need for digitally finding tooth features, such as the cusp tips, marginal ridges, central groove lines, buccal grooves, contact points, tooth axes system, etc., on a three-dimensional virtual dentition model of a patient.
U.S. Pat. No. 6,616,444 to Andreiko, et al. describes a system and method by which an orthodontic appliance is automatically designed and manufactured from digital lower jaw and tooth shape data of a patient. The method provides for scanning a model of the patient's mouth to produce two or three dimensional images and digitizing contours and selected points. A computer may be programmed to construct archforms and/or to calculate finish positions of the teeth, then to design an appliance to move the teeth to the calculated positions.
U.S. Pat. No. 6,322,359 to Jordan, et al. describes a computer implemented method of creating a dental model for use in dental articulation. The method provides a first set of digital data corresponding to an upper arch image of at least a portion of an upper dental arch of a patient, a second set of digital data corresponding to a lower arch image of at least a portion of a lower dental arch of the patient, and hinge axis data representative of the spatial orientation of at least one of the upper and lower dental arches relative to a condylar axis of the patient. A reference hinge axis is created relative to the upper and lower arch images based on the hinge axis data. Further, the method may include bite alignment data for use in aligning the lower and upper arch images. Yet further, the method may include providing data associated with condyle geometry of the patient, so as to provide limitations on the movement of at least the lower arch image when the arch images are displayed. Further, a wobbling technique may be used to determine an occlusal position of the lower and upper dental arches. Various computer implemented methods of dental articulation are also described. For example, such dental articulation methods may include moving at least one of the upper and lower arch images to simulate relative movement of one of the upper and lower dental arches of the patient, may include displaying another image with the upper and lower dental arches of the dental articulation model, and/or may include playing back recorded motion of a patient's mandible using the dental articulation model.
The invention disclosed herein offers a novel method and system for digitally finding tooth features, such as the cusp tips, marginal ridges, central groove lines, buccal grooves, contact points, tooth axes system, etc., on a three-dimensional virtual dentition model of a to patient.